We know that when Christ appears, we shall be like him,
for we shall see him as he is.
All who have this hope in him purify themselves,
just as he is pure.
This is not a religious thing, not some legalistic command accompanied by an angry face telling us to "Be pure!" It is a RESULT.
It is the RESULT of an GREAT DESIRE. Purity is a fruit of desire-attachment.
This GREAT DESIRE is TO BE LIKE HIM.
This GREAT DESIRE to BE LIKE HIM is fueled by a HOPE.
This HOPE is the expectation that one day WE SHALL SEE HIM as he is.
All who share this hope desire and admire Him and long to not only be with Him but to be like Him. We want to be like Jesus, not to impress anyone, but because we are His children and children want to be like their parents. Like Father, like daughters and sons.
I become what I long to behold. One day I shall behold Christ face to face. N.T. Wright writes:
"What an amazing moment! To come face to face, eye to eye, with the people he had loved but never seen. There is something transformative about eye contact. People who spend a lot of time looking at one another sometimes come to resemble each other. Perhaps this is because they are instinctively copying one another’s facial expressions until their muscles and tissue begin to be reshaped in that way. Imagine beginning that process at last after years of love which had been expressed through words and touch but never before through sight." (N.T. Wright, The Early Christian Letters for Everyone, p. 149)
Our deepest longing is to come face to face with Him. "To see his smile, to catch his facial expression, to begin to know him in a whole new way." (Ib.)
All who have this GREAT DESIRE purify themselves now as the RESULT of wanting to be like Him.
Purity is the result of a great longing.